This invention concerns cutting tools and more particularly knives for granulators, which are used to cut up plastic scrap into granules for use in recycling the plastic.
Granulators use elongated cutting knives mounted with bolts to a rotating cylinder, and a fixed bed knife past which the rotating knives cuts.
Large forces are generated such that the cutter knives must be rugged enough to be able to withstand high impact loads without cracking around the mounting holes. At the same time, because it is difficult to change knives, the wear resistance of the cutting edge is very important to reduce the downtime required to replace or resharpen the knives.
These requirements are somewhat at odds with each other, in that very hard, wear resistant alloys tend to be less ductile and more brittle, and thus less able to resist high peak loadings encountered so that breakage and cracking would be likely if a highly wear resistant material was used for the entire knife. Thus, a compromise in materials has heretofore been necessary, such that the wear resistant qualities of these knives is not optimal, and they must often be replaced or removed and resharpened.
It is the object of the present invention to provide a method of manufacturing cutting knives and more particularly granulator knives which method is economical and yet provides greatly improved wear resistance without increasing vulnerability of these knives to breakage and cracking.